232 research outputs found
Hormesis depends upon the life-stage and duration of exposure: examples for a pesticide and a nanomaterial
Tests to assess toxic effects on the reproduction of adult C. elegans after 72 h exposure for two chemicals,
(3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)), also known as diuron, and silver nanoparticles (Ag
NPs) indicated potential, although not significant hormesis. Follow up toxicity tests comparing the potential
hormesis concentrations with controls at high replication confirmed that the stimulatory effect
was repeatable and also statistically significant within the test. To understand the relevance of the
hormesis effects for overall population fitness, full life-cycle toxicity tests were conducted for each
chemical. When nematodes were exposed to DCMU over the full life-span, the hormesis effect for reproduction
seen in short-term tests was no longer evident. Further at the putative hormesis concentrations,
a negative effect of DCMU on time to maturation was also seen. For the Ag NPs, the EC50 for
effects on reproduction in the life-cycle exposure was substantially lower than in the short-term test, the
EC50s estimated by a three parameter log logistic model being 2.9 mg/L and 0.75 mg/L, respectively. This
suggests that the level of toxicity for Ag NPs for C. elegans reproduction is dependant on the life stage
exposed and possibly the duration of the exposure. Further, in the longer duration exposures, hormesis
effects on reproduction seen in the short-term exposures were no longer apparent. Instead, all concentrations
reduced both overall brood size and life-span. These results for both chemicals suggest that
the hormesis observed for a single endpoint in short-term exposure may be the result of a temporary
reallocation of resources between traits that are not sustained over the full life-time. Such reallocation is
consistent with energy budget theories for organisms subject to toxic stres
The Dream About the Magic Silver Bullet – the Complexity of Designing for Tablet-Mediated Learning
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